fix: isolate signal overlays from chart persistence

[jackhai9]

Temporary signal drawings trigger Binance chart-save callbacks even when excluded from saved chart JSON. Move Strategy27 event/compound markers and Strategy29/31 markers to a shared, pane-clipped SVG renderer so their updates no longer enter the native drawing/save pipeline. Keep signal thresholds, candle placement, retention, and trading behavior unchanged.

Preserve orderbook serialization batching while delivering every accepted default save callback with an independent snapshot. Explicit save signatures retain native behavior; cleanup preserves callback ownership and reports both action and serialization failures. Regression tests cover callback reentry, external wrappers, interval changes before the first marker, and stale rendering after failures.

Validation:

• Full Node/DOM suite: 2,079 passed.
• Affected orderbook browser scenarios: 68 passed.
• Continuous-readiness browser scenarios: 23 passed. A controlled delayed response reproduces and fixes the CI test race between response completion and the paused virtual clock; production trading logic is unchanged.
• SVG browser scenarios: 3 passed, including Strategy27 labels/arrows, independent layers, zero native drawing/save calls, and isolated cross-page IndexedDB readback; screenshot inspected.
• Generated all affected installers; test lint, syntax checks, and diff checks passed.
• Independent review performed; findings fixed and rechecked before merge.

Versions: orderbook 2.7.217, Strategy27 0.6.8, Strategy29 0.5.8, Strategy31 0.1.2.

This removes verified marker-generated save traffic and callback loss; it does not establish that every Chrome IndexedDB stall is fixed. Live installation/readback follows publication. The active US trading task will not be interrupted for validation. No live financial actions are included.